1. Field of the Invention
The present disclosure relates to a fuel cell separator and a fuel cell including the fuel cell separator, and particularly to the configuration of the fuel cell separator.
2. Description of the Related Art
A polymer electrolyte fuel cell (hereinafter referred to as “PEFC”) causes a hydrogen-containing fuel gas and an oxygen-containing oxidizing gas, such as air, to electrochemically react with each other to generate electric power and heat at the same time. A single cell (cell) of the PEFC includes an MEA (Membrane-Electrode Assembly), gaskets, and electrically-conductive plate-shaped separators. The MEA includes a polymer electrolyte membrane and a pair of gas diffusion electrodes (an anode and a cathode). Generally, the PEFC is configured such that a plurality of cells are stacked on one another, end plates sandwich the stacked cells from both sides of the stacked cells, and the end plates and the cells are fastened by fastening members.
In a case where the polymer electrolyte membrane contains moisture so as to be saturated, a specific resistance thereof lowers, and the polymer electrolyte membrane serves as an electrolyte having hydrogen ion conductivity. Therefore, during an electric power generating operation, reactant gases (the fuel gas and the oxidizing gas) are humidified and then supplied to the PEFC. Moreover, during the electric power generating operation of the PEFC, water is generated as a reaction product in the cathode by the oxidation of the hydrogen. The water in the humidified reactant gas and the water as the reaction product contribute to the realization of the saturation of the moisture content of the polymer electrolyte membrane. The surplus water is discharged to outside of the PEFC together with the surplus anode and cathode gases.
The performance of the PEFC is greatly influenced by appropriate management of the steam and the produced water used for humidifying the reactant gases. In a case where the produced water or condensed water stays at a specific region, the reactant gas cannot be supplied to the electrode corresponding to the region, and this causes deterioration of a cell performance (so-called flooding). Moreover, in a case where a humidification amount (steam content) of the reactant gas to be supplied to the PEFC is small (in a case where the PEFC is operated under a so-called low humidification condition), the deterioration of the cell performance occurs by the reduction in the moisture content of the polymer electrolyte membrane in the vicinity of a portion of the gas diffusion electrode to which portion the reactant gas is supplied at first (this is called dry up).
To solve such problems, the shapes of the gas channels are devised to discharge the surplus moisture in the cell to outside. Or, the water is moved to a portion of the same cell in which portion the water is scarce. Thus, approaches to solve the problems, such as the flooding and the dry up has been performed (see Document 1 (Japanese Laid-Open Patent Application Publication No. 2005-158513) and Document 2 (Japanese Laid-Open Patent Application Publication No. 2006-236750) for example).
In the fuel cell disclosed in Document 1, a fine groove extending along an upstream side to downstream side of a reactant gas channel is formed at a rib portion of the separator which portion contacts the MEA. This intends to remove the produced water and the condensed water by guiding the water to the fine groove, and move the water at the downstream side where the water tends to be excessive to the upstream side where the water tends to be scarce.
Moreover, in the fuel cell separator disclosed in Document 2, a water reservoir groove is formed to extend in parallel with the gas channel. This intends to move the water at the downstream side to a locally dry region of the upstream side.
However, the present inventors have found that even in the fuel cell disclosed in Document 1 and the fuel cell separator disclosed in Document 2, there is still room for improvement in light of the improvement of the cell performance when the electric power generation is carried out using the reactant gases which are low in humidity. To be specific, in the fuel cell disclosed in Document 1 and the fuel cell separator disclosed in Document 2, in a case where the fuel cell generates the electric power under such an operating condition that the downstream region is surely saturated, the surplus water existing as the water may be able to be moved to the upstream side through the fine groove or the water reservoir groove. However, if the downstream region is not saturated even in consideration of the produced water and the gas consumption, the moisture is not moved through these grooves to the upstream, so that the cell performance cannot be adequately improved.
Moreover, in a case where the number of fine grooves is one as in the case of the fuel cell disclosed in Document 1, and the fine groove is clogged by the accumulation of the produced water, the reactant gas cannot flow through a portion of the fine groove which portion is located on the downstream side of the clogged portion, since there is no place to which the produced water is evacuated. Therefore, in the fuel cell disclosed in Document 1, the reactant gas cannot be adequately supplied to the gas diffusion electrode facing this portion, so that the cell performance cannot be adequately improved.
Moreover, in the fuel cell separator disclosed in Document 2, since a water reservoir groove is not communicated with a reactant gas supplying manifold hole and a reactant gas discharging manifold hole, the reactant gas is not directly supplied to the water reservoir groove. Therefore, the reactant gas cannot be adequately supplied to the gas diffusion electrode facing the water reservoir groove, so that the cell performance cannot be adequately improved.
The present disclosure was made to solve the above problems, and an object of the present disclosure is to provide a fuel cell separator capable of producing a high-humidity high-gas-concentration electrode region especially in a case where the PEFC is operated under the low humidification condition and adequately improving the cell performance, and a fuel cell including the fuel cell separator.